The present invention relates to magnetic memory devices, and more specifically, to thermally-assisted magnetoresistive random access memory (TAS-MRAM) devices that provide lower thermal conductivity.
Magnetoresistive random access memory (MRAM) is a non-volatile computer memory (NVRAM) technology. Unlike conventional RAM chip technologies, MRAM data is not stored as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic layers, each of which can hold a magnetic field, separated by a thin insulating layer. One of the two layers is a reference magnet set to a particular polarity, while the remaining layer's field can be changed to match that of an external field to store memory and is termed the “free magnet” or “free-layer”. This configuration is known as a magnetic tunnel junction (MTJ) and is the simplest structure for a MRAM bit. A memory device is built from a grid of such “cells.” In some configurations of MRAM, such as the type further discussed herein, both the reference and free layers of the magnetic tunnel junctions can be switched using an external magnetic field.
A variation of MRAM technology includes a thermally-assisted magnetoresistive random access memory (TAS-MRAM). A TAS-MRAM device requires heating of the magnetic tunnel junction stack to a write temperature (Twrite) higher than the operating temperature (Top) in order to write the device. The increased write temperature is typically achieved by Joule heating using a bias current that is applied during the write process. The amount of power required to heat the device to Twrite depends strongly on the thermal conductivity between the device/surrounding structures and the substrate. Conventional TAS-MRAM devices are susceptible to large amounts of thermal leakage at the magnetic tunnel junction. Consequently, the power necessary to achieve Twrite for a device having a large number of devices and surrounding structures can be undesirably large to compensate for the thermal leakage.